igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Often found in oceanic crust and huge flood basalt provinces.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for fiber production (basalt fiber) and as decorative stone.
Geological facts
Basalt is the most common rock type in Earth's crust and covers most of the ocean floor. It is also found in large quantities on the Moon and Mars.
Field identification & locations
Identify by its heavy weight (high density), dark color, and very fine-grained texture that lacks visible crystals. Often shows vesicular (gas bubble) holes or columnar jointing in the field.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
Igneous
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral